1. Field of the Invention
This invention relates to an apparatus for inspecting the surface of materials, which enables to rapidly and surely measure and estimate materials such as crystalline materials for their surface defects.
2. Prior Art
There have heretofore been known apparatus for measuring and observing materials, such as crystalline materials e.g. semiconductor wafers, to know the surface defects and the like of said materials. For example, Japanese Pat. Appln. Laid-Open Gazette No. Sho 60-101942 (No. 101942/1985) discloses an apparatus for measuring and observing defects such as etch pits (recesses or grooves caused by the defects of crystals) produced by subjecting a wafer-like sample (an object to be inspected) to etching or other treatments.
The structure of a conventional apparatus for measuring and observing such defects of crystalline materials as the above is roughly shown in FIG. 19 of the accompanying drawings.
In FIG. 19, numeral 1 indicates a wafer sample which has been subjected to etching, as an object to be examined for measurement and estimation, and numeral 2 a stage on which the wafer sample 1 is mounted. This stage 2 is constructed so that it can be moved in the longitudinal direction (X direction which is vertical to the surface of paper having said FIG. drawn thereon), in the lateral direction (Y direction which is the left- and right-side direction in said FIG.) and in the height direction which is the upper-and-lower direction in said FIG. To allow the stage 2 to be movable in these directions, the stage 2 is provided with drive mechanisms 2b, 2c and 2d each having a pulse motor (stepping motor) and the like. Numeral 3 indicates a pulse motor controller which sends a drive signal to each of the pulse motors of the mechanisms 2b, 2c and 2d in the directions X, Y and Z; and numeral 13, a pulse motor driver which outputs pulse signals to the pulse motors according to drive signals outputted from the pulse motor controller 3.
Numeral 4 indicates a microscope for observing and measuring the wafer sample 1 mounted on the stage 2. This microscope 4 is fitted with an illumination lamp (halogen lamp) 5 which is a light source for lighting up the sample 1, and with a TV camera 6 for photographing a stationary image of the sample 1. Numeral 14 indicates a microscope control unit for controlling an autofocus mechanism of the microscope 4.
Numeral 7 indicates an image processing unit for estimating defects of the sample 1, such as etch pits, on the basis of image data inputted by the TV camera 6; numeral 8, a computer for controlling communication between the pulse motor controller 3 and the image processing unit 7, and for manipulation of data obtained from the image processing unit; and numeral 9, a monitor for displaying image data obtained from the image processing unit 7.
With the conventional apparatus having such a structure as above, the surfaces of samples are inspected as follows.
First of all, the sample 1 is set on the stage 2. The computer 8 gives instructions to the pulse motor controller 3 to move and stop the stage 2 at a predetermined position. Then, there is procured an enlarged image of the sample 1 obtained through the microscope 4 under the lighting lamp 5. The enlarged image so procured is inputted, as image data, through the TV camera 6 to the image processing unit 7. Thereafter, the image data is subjected to image processing at the image processing unit 7 and the computer 8 to measure (calculate) and estimate the distribution, number, shape, density and the like of defects or imperfections contained in or on crystals.
After the end of the above processes or treatments, the stage 2 with the sample 1 mounted thereon is moved to the next position for measurement whereupon the sample 1 in the stationary state is subjected to the same processes as above thereby to measure and evaluate the defects of the wafer sample.
FIG. 20A shows how the entire surface of the wafer sample 1 is inspected. In this Fig., each of rectangles 41 indicates a unit area for observation, this observation unit area enabling a magnified image thereof to be obtained through the microscope, in other words, an observation unit area enabling image data thereof to be fetched at one time (for example, an observation unit area such as 0.5 mm.times.0.5 or 1 mm.times.1 mm). The stage 2 is so moved as to make a measurement of each rectangle 41 one by one in the order indicated by an arrow mark 42 so as to measure the entire surface of the wafer sample 1 for defects.
FIG. 20B shows how the predetermined unit areas of the wafer sample 1 are measured. Each of rectangles 43 indicates an observation unit area which enables a magnified image thereof to be obtained through the same microscope 4 as used for the rectangles 41 in FIG. 20A. The stage 2 is so moved as to measure the rectangular areas 43, which are observation unit areas, one by one so as to measure these unit areas of the wafer sample 1 for their defects.
In the aforementioned conventional apparatuses for inspecting the surface of materials, the stage 2 is once stopped when image data is obtained and the thus obtained image data is processed during the stoppage of the stage 2 so that it is impossible to increase the average moving speed of the stage. In addition, movement of the stage and processing of the image data are not carried out simultaneously, but they are done respectively at different times. Accordingly, it takes a long time for one sample to be measured and, therefore, this decreases the capability of measurement of the apparatuses and processing particularly when measurement is made on the entire surface of a wafer sample as shown in FIG. 20A. For example, in the case where the entire surface of a semiconductor having a 6-inch diameter was measured using a conventional commercially available apparatus, the time needed for the measurement was about 10 hours.
Further, in cases where a wafer sample to be inspected has foreign matters, such as dust, attached thereto and the wafer sample has flows on the surface, it is difficult to distinguish these dust and flaws from the etch pits to be inspected. Even if the image processing unit 7 and computer 8 were used to try to distinguish etch pits from other things, sufficient distinction therebetween would be impossible.